1. Field of the Invention
This invention relates to a catalytic absorbent composition, its preparation, and use for desulfurizing hydrocarbon oils, and most particularly to the use of the composition for desulfurizing reformer feedstocks.
2. Description of the Prior Art
Catalysts containing sulfur-sensitive Group VIII metal components are often employed in petroleum refining processes such as hydrocracking, synthesis gas processing, methanation, reforming, steam reforming, hydrogenation, and the like. Such catalysts lose their catalytic activity and stability due to deleterious effects of sulfur during processing. In a typical reforming process treating a straight run naphtha or cracked naphtha, the feedstock is upgraded (as by increasing the octane number of the gasoline fraction) by contact with a catalyst comprising a noble metal on alumina. Conditions utilized in reforming processes vary depending upon such factors as the type of feed processed and the desired increase in octane level.
To achieve maximum run lengths and increase process efficiency, it is generally recognized that the sulfur content of the feedstock must be minimized. Reforming catalysts, and particularly those comprising platinum, and even more particularly comprising platinum and rhenium, deactivate rapidly and are even poisoned in the presence of sulfur compounds. As a result, it is necessary to reduce the sulfur content of reformer feedstocks as low as possible. Preferably, feedstocks contacted with reforming catalysts are desulfurized to contain less than about 0.5 ppmw sulfur.
A common method of treating reformer feeds to reduce the sulfur content is by hydrodesulfurization wherein a naphtha or other hydrocarbon feedstock is contacted with a sulfur-tolerant hydrogenation catalyst in the presence of hydrogen. Although good sulfur removal may be achieved by hydrodesulfurization units operating under severe conditions, the efficiency of such processes is ultimately limited by equilibrium and/or kinetic considerations. In many instances, it is not possible to obtain hydrodesulfurized products containing less than 0.1 ppmw sulfur as desired in most reforming operations. Furthermore, it is impossible to guard against occasional upsets in the hydrodesulfurization unit which can result in higher than desired levels of organosulfur compounds remaining in the reformer feedstock.
In addition to hydrodesulfurization, there are other processes employing catalytically active materials for removing sulfur from hydrocarbons. Such processes reduce the sulfur content of the hydrocarbon by "absorbing" sulfur therefrom and generally employ a catalytically active absorbent material under nonhydrogenative conditions. Typically, nonhydrogenative conditions include contact of the absorbent material with the feedstock in the absence of hydrogen; however, if desired, hydrogen is sometimes present, but only in amounts or under conditions that prevent essentially any hydrogenation of the organosulfur components in the feedstock. Usually, the absorbent material contains a metal component, such a nickel, copper, or silver, and the feedstocks generally treated are reformer feedstocks, particularly naphthas. Typical of such processes include that disclosed in U.S. Pat. No. 2,755,226 to Annable wherein a bed of copper molybdate pellets is utilized to reduce the sulfur content of naphthas. Similarly, in U.S. Pat. No. 4,224,191 to Bishop III, the use of copper components supported in conventional carriers is disclosed for reducing the sulfur content of reformer feedstreams. However, the search continues for catalytically active absorbent materials which are more active and which have more capacity for the absorption of sulfur than the materials of the prior art.
Accordingly, it is an object of the present invention to provide a novel composition useful for desulfurizing hydrocarbon oils.
It is a further object of the present invention to provide a method for preparing a composition useful for desulfurizing hydrocarbon oils.
Another object of the present invention is to provide a method for upgrading a hydrocarbon oil by contact with a novel composition of the present invention.
These and other objects and advantages of the invention will become apparent from the following description.